The color output of a printing machine may drift over time. The quality of printed images that are output by a printing machine can be maintained by periodically performing a color validation process which involves having the printing machine print a color test pattern. The color test pattern includes color patches, each or which are expected to have a target color property. After printing, the color properties of the color patches are measured and compared with the target properties. If measurements do not match the target properties, then an alert is generated and/or a color calibration process can be performed in which operational parameters of the printing machine are adjusted.
During measurement, light is directed onto the sheet on which color patches were printed. Light reflected from a subject color patch is picked up by a sensor to reveal the color property the color patch. However, the sensor can also pick up light reflected from areas of the printed sheet that surround the sensor. The light reflected from surrounding areas, referred to as flare, can introduce inaccuracies in the measurement for the subject color patch. There is a continuing need to improve the quality of printed images and, particularly, a need to reduce inaccuracies related to flare.